All-dielectric terahertz metasurface for linearly-polarized multichannel transmission and superposition states of spherical and vortex waves

Compared to pure vortex waves,the superposition state of spherical waves and vortex waves has enough degrees of freedom to upgrade applications in particle manipulation,information encryption,and large-capacity communications.Here,we propose a new scheme to achieve superposition states and multichannel transmission of vortex and spherical waves.Two transmissive all-silicon metasurfaces that enable mutual interference between linearly polarized(LP)waves in the terahertz region are demonstrated.Type A can achieve interference between x and y polarized waves,while type B can achieve interference between x(or y)and x(or y)polarized waves.The multichannel transmission and superposition states of topological charges of+3,+2,and+4 are designed and demonstrated from theoretical,simulative,and experimental perspectives at 1.1 THz.In addition,the objective fact that the focused superposition state must be observed close to the focal plane is also revealed.The measured results are in good agreement with the theoretical and simulative results.This work provides an idea for the design of ultrathin terahertz devices and could be applied in the fields of information encryption and highfrequency communications.